WASHINGTON, March 15-- The United States will "have to negotiate" with the Syrian government in an effort to end the country's four-year-old conflict, Secretary of State John Kerry said in a TV program aired on Sunday.

"We have to negotiate in the end," the top American envoy told CBS News in an interview on the occasion of the fourth anniversary of the conflict, adding "We've always been willing to negotiate in the context of the Geneva I process."

Two rounds of Geneva peace talks, held respectively in June 2012 and January 2014, had failed to end the fighting in Syria, where some 220,000 people have been killed and about half of the population forced to flee their homes, with 4 million landing in refugee camps in neighboring countries.

Kerry blamed the lack of interest in negotiations on the part of Syrian President Bashar al-Assad for the collapse of the last round of Geneva talks.

He said: "Assad didn't want to negotiate. What we're pushing for is to get him to come and do that."

"We are working very hard with other interested parties to see if we can reignite a diplomatic outcome," he added. "Everybody agrees there is no military solution; there's only a political solution."

The Obama administration's policy on Syria is coming under growing scrutiny both at home and abroad, as it had insisted early on on al-Assad's ouster as part of any settlement but has remained mute on the issue since it launched air raids on the extremist Islamic State group inside both Iraq and Syria last year.

State Department spokeswoman Marie Harf insisted that the U.S. policy toward Syria has not changed.

"Policy remains same & is clear: there's no future for Assad in Syria & we say so all the time," she tweeted. "@JohnKerry repeated long-standing policy that we need negotiated process w/regime at table - did not say we wld negotiate directly w/Assad."